The present invention relates to a method of locally cleaning surfaces of parts in the primary circuit of a nuclear reactor, i.e., in connection with inspection of the surfaces, which surfaces are coated with corrosion products, primarily oxides.
The primary circuit in a boiling water reactor is the circuit in which steam generated in the reactor vessel is passed to a steam turbine, from there to a condenser, and in which water formed in the condenser is returned to the reactor vessel. The primary circuit in a pressurized water reactor is the circuit in which water heated in the reactor vessel is passed to a steam generator and from there is returned to the reactor vessel. In case of recurring inspection of nuclear reactors, which is normally carried out when the reactors are shut down for refuelling, surfaces of the reactor vessel and of other parts including in the primary circuit are examined in order to determine, among other things, whether any cracks have formed in the construction material. The examination is often carried out with the aid of a TV camera while the examined surface is situated below the surface of the reactor water in the reactor vessel or in the reactor pool. Those metal surfaces, which are in contact with the reactor water during operation of the reactor, and particularly those surfaces which are in contact with high temperature water, are coated with a film of corrosion products, mostly oxides. Scrape marks and certain optical effects in the film are readily perceived as cracks in the construction material. The evaluation of an optical inspection can therefore be made more reliable if it can be performed on a metallically clean surface. Mechanical cleaning methods, such as grinding, blasting or brushing to remove the oxide, leave such tracks in the metallic surface as to render an optical inspection unreliable.